I. Field of the Invention
The present invention relates to the field of batteries, and more specifically, to battery configurations with multiple series or combination series and parallel cell arrangements.
II. Related Art
Batteries and battery xe2x80x9cpacksxe2x80x9d using a variety of battery or cell configurations act as the necessary power source for many modern products. They are a critical component of portable electronic devices, such as cellular telephones, laptop computers, compact disc (CD) players, and similar types of battery-operated devices. The longer a particular battery or configuration of batteries can provide power to a cell phone or laptop the longer a user is able to enjoy use of those items. Moreover, the shorter the time it takes to charge a battery configuration, the sooner the user is able to use those items away from a power outlet.
The term xe2x80x9cbattery packxe2x80x9d herein refers to a variety of battery configurations which employ multiple cells configured in series, or cells arranged in a combination of series and parallel configurations.
Ideally, the cells in the battery pack that are arranged in series would have exactly the same voltage and, therefore, be in balance.
Because each cell in a given battery pack has slightly different charge and discharge characteristics in real applications, the cells will eventually become unbalanced as they are discharged and recharged. Typically, as the number of charge and discharge cycles increases, the level of imbalance increases.
Typical charging circuitry is unable to fully charge the configuration because of the imbalance. This reduces the usable capacity of the battery pack, eventually, causing the battery pack to become useless.
There are other techniques in use for voltage balancing. However, many are either complex or expensive or both. What is, therefore, desired is a simple and inexpensive battery pack with a method and apparatus to maintain the balance between the cells.
The present invention provides a simple and inexpensive method and apparatus which can be incorporated in a battery pack or directly in an electric or electronic device, that maintains charge balance between the cells within, thereby increasing the usable life of the battery pack and the usage time of the powered product. Individual cell voltages within a pack and the total voltage of the battery pack are monitored by an op-amp having at least a positive input terminal, a negative input terminal and an output terminal. Terminal is well known in the art to mean a variety of physical forms by which electrical connections are made. The final form of the terminal will be determined by those skilled in the art as to the actual connection method used. An example of terminals might be, a screw terminal, a wire wrap, or a solder pad. A comparison to the desired voltage is made by the op-amp and corrective current is then injected or removed by the op-amp from appropriate positions within the battery pack to balance or maintain the individual cell voltages.
The invention utilizes a low power op-amp to compare the voltage at the junction between the series battery cells to the total voltage. The connection point between the cells being balanced is referred to as the inter-cell interface. If the cells are balanced this voltage will be a fraction of the total voltage. As an example, with two cells the voltage would be one half the total voltage. With three cells the total would be one third the total voltage. If the voltage at the junction does not equal the appropriate fraction of the total voltage, current is injected or withdrawn until balance is achieved.
The invention can continue to perform the monitoring and maintaining of the cell balance during storage, as well as during charging and discharging of the cells.